In the drilling of certain earth bore holes, both on shore and off shore, in the oil and gas well drilling industry, the practice is to initially drill a large surface bore hole in which a large surface pipe is to be set to form a section of surface casing. The large bore hole and casing may be on the order of 60" in diameter.
The drilling of such large bore holes requires the use of large drill bits and the application of large weight to the drill bits as they are being conventionally rotated to drill through the earth formation, during the circulation of drilling fluid, which is employed to also flush the cuttings from the bore hole.